Intramolecular Cyclization of Nerol and the Related Attack of (Z)-Allylic Alcohol Moiety on the Terminal Olefin Linkage as Induced by TiCl4–PhNHMe Complex. Synthesis of Nezukone

Nerol was cyclized to terpinyl chloride or bromide in the presence of TiX4–PhNHMe (1 : 1) complex (I, X= Cl, Br) in dichloromethane at −23 °C, geraniol being converted into geranyl halide by simple halogenation. Terminally modified derivatives YCH2C(Me)=CHCH2CH2CMe=CHCH2OH (Y=SiMe3, SnBu3) of (2Z,6E) configuration were cyclized by treatment with I to afford limonene in high yields and 100% selectivity. Cyclization of (2Z) isomers of CH2=CR–CH2CH2CMe=CHCH2OH (R=H, Me, Cl) produced seven-membered carbocyclic products in fair yields. The novel procedure has been utilized in the synthesis of nezukone from (2E)-3-isopropyl-2,6-heptadien-1-ol involving five steps.

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